Photo-imaging utilizing uranyl compounds

ABSTRACT

Imagewise light exposure of a layer of a composition comprising a uranyl compound and an hydroxyl-containing compound results in photolytic reduction of uranyl ions which, upon subsequent contact with a developer fluid containing ferricyanide ions, form an imagewise deposition of a distinct uranyl ferrocyanide color body. Application of a toning fluid containing ferric ions may subsequently be employed to achieve neutral image tones.

nite States Levinos Dec. 3, 1974 I PHOTO-IMAGING UTILIZING URANYLCOMPOUNDS [75] Inventor: Steven Levinos, Chatham, NJ.

[73] Assignee: Keuffel & Esser Company,

Morristown, NJ.

22 Filed: Aug. 24, 1972 21 Appl. No.: 283,465

[52] US. Cl. 96/48 R, 96/88 v [51] Int. Cl G03c 5/24, G03c 1/00 {58]Field 0fSear1:h..... 96/88, 48 R, 48 PD [56] References Cited UNITEDSTATES PATENTS 7/1986 Ravich 96/90 R 3/1960 Jonker et al 96/48 PD OTHERPUBLICATIONS British Journal of Photography, Vol. LXXXVI, Mar. 24, 1939,page 186.

Primary Exunu'm'rRonald H. Smith Assistant Examiner-Won H. Louie, Jr.

Attorney, Agent, or Firm-Lionel N. White, Esq.

[ 5 7] ABSTRACT color body. Application of a toning'fluid containingferric ions may subsequently be employed to achieve neutral image tones.

4 Claims, No Drawings PHOTO-IMAGING UTILIZING URANYL COMPOUNDS SUMMARYThe present invention provides a photoimaging material which comprises asupporting sheet member selected from any of a host of common webmaterials such as paper, plastic film and the like, a coating of aphoto-sensitive composition comprising a uranyl compound, and a sourceof hydroxyl groups. Upon imagewise exposure to actinic radiation,preferably in the region of ultraviolet light, there'occurs in thematerial a photolytic redox reaction wherein the uranyl ions in theexposed areas are reduced to the uranous form by abstraction ofelectrons from available hydroxyl groups. The source of such groups maybe conveniently included in a coating composition in the form offilmforming binder materials such as polyvinyl alcohol, hydroxyethylcellulose and the like, and thus serve a dual function in theprocedureof the present invention. A useful alternative to binders forthis purpose is the employment of surface saponification of filmsupports such as cellulose acetate- Subsequent to imagewise lightexposure, the material of the present invention is contacted with adeveloping fluid containing ferricyanide ions, for example by theapplication of an aqueous solution of an alkali metal ferricyanide. Theresulting oxidation of the photolytically generated uranous ions to theuranyl state and concurrent reduction of the ferricyanide ions toferrocyanide yield, in light exposed areas, substantially insolubledistinctly colored uranyl ferrocyanide. A water rinse thereafter removesthe excess developer solution and the vestiges of the originalwater-soluble uranyl compound from the unexposed areas of the imagingmaterial. Thus, there remains on the carrier sheet the imagewise depositof the distinctly colored uranyl ferrocyanide color body.

In further application of thepresent invention, the image may beprovided in a more neutral blue-black tone by the application of asolution comprising ferric ions, for example an aqueous solution offerric nitrate.

The resulting metathetic formation of ferric ferrocya nide in the imageareas not only provides the more pleasing tone but also yields an imagewhich is less moisture sensitive and thus more permanent.

In addition to the more simple material thus far noted, the presentinvention provides a means for sig nificantly sensitizing thecomposition by the incorporation of formic acid salts which contributeto the photolytic reduction of the uranyl ions of thecomposition. Inthis manner, a composition of a uranyl compound in a binder materialcomprising hydroxyl groups may be greatly increased in light sensitivityby the addition of sodium, potassium, or ammonium formate which,apparently upon the photolytic decomposition of formic acid, furtherpromotes the reduction of the uranyl ions to the uranous form, therebysubstantially increasing the density of photoformed reducing centers.

DESCRIPTION hydroxyl-containing substantially water-dispersible bindermaterials are available and, in addition to those previously noted,include hyd'roxypropyl cellulose and sodium carboxymethyl cellulose.

In order to take advantage of the aqueous medium employed in thesensitizing compositions and to effectively insure an intimatecombination of the cationic uranium with the source of hydroxyl groups,any of the numerous water-soluble uranyl compounds are employed. Theseinclude the acetate, nitrate, chloride, sulfate, formate, propionate,succinate, glutarate and phenyl acetate. The simple combination of theuranyl salt in aqueous solution with a selected binder provides acoatable composition useful in the preparation of the instant imagingmaterials.

It is to be noted that the cellulosic character of paper fibers and thesaponified surfaces of cellulose ester film base materials to asignificant extent provide the hydroxyl-containing component of thepresent imaging materials. Additional useful sources of this componentare represented in humectant adjuncts such as glycerin and ethyleneglycols, which materials also provide for the maintenance of substantialmoisture in the imaging sheet. It has been observed that such moistureeffectively assists in the image-forming process.

The earlier-noted chemical sensitization achieved through the additionof water soluble formate salts takes advantage of the aqueous nature ofthe sensitizing composition. It should be pointed out, however, that anacidic pH is preferably maintained in the coating composition in orderto prevent the formation of insoluble basic uranyl compounds.

In use, the imaging material of the present invention is exposedimage-wise to light, preferably of the ultraviolet region, in the mannerof utilizing sources common to normal photoimaging procedures. In areasof the imaging material thus exposed to photolytic radiation, the uranylions are reduced to a lower valence form, for example the uranous form,by acquisition of electrons from the hydroxyl groups of the base, thebinder material, or the humectant adjuncts. It has been found that theuranous form of the compounds included in the imaging material are lesswater soluble than the uranyl form and on this basis an improvement inthe background areas of the final image may be attained through the useof a short water rinse immediately following the light exposure step.Thus, a substantial amount of the original uranyl compound is removedfrom the material and is not available for vagrant formation of thecolor body during the development step.

In order to form a distinct color body which will define the lightexposure image, the exposed material is contacted with a solutioncontaining ferricyanide ions, for example an aqueous solution of analkali metal fer ricyanide. From the concurrent oxidation of the uranousions and reduction of the ferricyanide ions, there results the formationof an imagewise disposition of the distinctly colored insoluble uranylferrocyanide in the following manner: j

The developed image sheet is again subsequently rinsed with water toremove the unused development solution as well as any uranylferricyanide which forms in the unexposed areas of the imaged material.It

sure. That is not to say that some time span may not occur between theexposure and development step, since the noted degradation of theuranous ion, i.e., its reversion to the uranyl form by aerial oxidation,requires a few hours to be of any consequence.

The developed uranyl ferrocyanide image is of a brown tone which may notbe as preferred in ultimate use as the more neutral blue-black tonesobtained with many conventional imaging processes. For this reason theimaged material may be subjected to an additional toning step whichcomprises application of an aqueous solution of a ferric salt. Bymetathesis the ferric ions replace the uranyl ions and the compositionof the image acquires a significant proportion of the blue ferricferrocyanide color body. The final image tone is, of course, regulatedsimply by the extent of time allowed for the toning step. A final waterwash and drying complete the processing and yield a permanent,well-toned image.

PREFERRED EMBODIMENTS Example 1 v A solution was prepared of thefollowing composition:

Uranyl nitrate 6H,O Deionized water 4 Glycerin A sheet of filter paperwas immersed in the solution and allowed to dry at normal roomconditions under yellow safe light. In the meantime, a similarcomposition was prepared and one gram of sodium formate was added. Thesolution remained clear and thus was evidently sufficiently acid that nobasic uranyl salt was present. Using filter paper, imaging material waslikewise prepared with this solution. The sheets were individuallyexposed through an opaque stencil to the light from a bank of blacklight" lamps (GE F8T5 BLB) at a distance of about 2 cm. After exposure,the sheets were rinsed in clear water for about 15 seconds and'thenimmersed in a aqueous solution of potassium ferricyanide for aboutseconds. A red-brown image was formed in the light exposed areas and afinal water rinse of about 15 seconds completed the imaging process. Inorder to achieve image densities of substantial equivalence, thematerial of this example devoid of the formate salt was exposed forabout 2 minutes while that including the formate accelerator was exposedfor only 1 minute. Example 2 A sheet of porous paper (filter paper) wassaturated with the following solution and dried under subdued light atnormal room conditions:

Uranyl acetate 2H,O(8% aq. sol.) 2 Sodium formate Glycerin Dilute formicacid to clear solution (pH 4.2)

Portions of the resulting sheet were individually exposed through anopaque stencil for about one minute as in Example 1 and for about oneminute to a source of substantial visible actinic radiation (500-wattphotoflood lamp) at a distance of about 15 cm. After a short waterrinse, the exposed sheets were immersed in a 5% solution of potassiumferricyanide for about 15 seconds and were then rinsed with water toyield equally dense red-brown images in the light-exposed areas. Thesheets were then immersed for about 15 seconds in a 5% aqueous solutionof ferric nitrate 9H O, followed by a water rinse to yield similarneutral blue-black tone images.

Example 3 The following coating composition was prepared:

Deionized water 95.0 ml. Hydroxypropyl cellulose 5.0 g. Uranyl nitrate6H O 2.5 g. Glycerin 1.0 g. Sodium formate l.0 g.

The resulting solution was coated on a baryta-surfaced sheet commonlyemployed in the preparation of photographic materials to a wet thicknessof about 130 microns. After drying at normal room conditions underyellow safe lights, the sheet was exposed for seconds through an opaquemetal stencil to light from the black light arrangement of Example 1.Development treatment with 5% aqueous potassium ferricyanide and toningwith 5% aqueous potassium ferricyanide and toning with 5% aqueous ferricnitrate provided a dense, neutral-toned image.

What is claimed is:

1. Imaging material comprising a support and a coating thereon of alight-sensitive composition consisting essentially of a water-solubleuranyl compound and a water-soluble formate salt in intimate admixturewith a substantially water-dispersible film-forming binder selected fromthe group consisting of polyvinyl alcohol, hydroxyethyl cellulose,hydroxypropyl cellulose, hydroxymethyl cellulose, sodium carboxymethylcellulose, and saponified cellulose esters.

2. The method of forming a visible image comprising:

a. exposing imagewise to light sheet material according to claim 1; and

b. contacting at least the light exposed areas of said material with adeveloping fluid comprising ferricyanide ions, thereby forming adistinct imagedefining color body in said light-exposed areas.

3. A method according to claim 2 which further comprises contacting atleast said image-defining color body with a toning fluid comprisingferric ions, thereby to provide a neutral-toned image in saidlight-exposed areas.

4. A method according to claim 3 wherein said developing fluid comprisesan aqueous solution of a ferricyanide salt, and said toning fluidcomprises an aqueous solution of a ferric salt, which method furthercomprises the steps of rinsing said sheet material with waterimmediately subsequent to each of the light exposing,

developing, and toning steps.

1. IMAGING MATERIAL COMPRISING A SUPPORT AND A COATING THEREON OF ALIGHT-SENSITIVE COMPOSITION CONSISTING ESSENTIALLY OF A WATER-SOLUBLEURANYL COMPOUND AND A WATER-SOLUBLE FORMATE SALT IN INTIMATE ADMIXTUREWITH A SUBSTANTIALLY WATERDISPERSIBLE FILM-FORMING BINDER SELECTED FROMTHE GROUP CONSISTING OF POLYVINYL ALCOHOL, HYDROXYETHYL CELLULOSE,HYDROXYPROPYL CELLULOSE, HYDROXYMETHYL CELLULOSE, SODIUM CARBOXYMETHYLCELLULOSE, AND SAPONIFIED CELLULOSE ESTERS.
 2. The method of forming avisible image comprising: a. exposing imagewise to light sheet materialaccording to claim 1; and b. contacting at least the light exposed areasof said material with a developing fluid comprising ferricyanide ions,thereby forming a distinct image-defining color body in saidlight-exposed areas.
 3. A method according to claim 2 which furthercomprises contacting at least said image-defining color body with atoning fluid comprising ferric ions, thereby to provide a neutral-tonedimage in said light-exposed areas.
 4. A method according to claim 3wherein said developing fluid comprises an aqueous solution of aferricyanide salt, and said toning fluid comprises an aqueous solutionof a ferric salt, which method further comprises the steps of rinsingsaid sheet material with water immediately subsequent to each of thelight exposing, developing, and toning steps.